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Video: Live underwater video of Gulf oil leak

HOUSTON — After a government review concluded that pressure tests of a new containment cap would not make the Gulf oil spill worse, BP on Wednesday started the process to begin testing — raising hopes once again that the flow could be stopped nearly three months after the Deepwater Horizon rig explosion.

Kent Wells, a BP senior vice president, said at a Wednesday evening news briefing that the valve on the top portion of the cap had been shut, meaning the oil had stopped pouring out from there. Live video of the cap a mile below the Gulf surface confirmed a significantly reduced flow.

The full "integrity test" will begin when the flow of oil stops coming out of the cap, a BP spokesman told NBC News.

On its Twitter feed Wednesday, BP reported a leak was detected and isolated in a pipe on the cap and the test won't begin until that is repaired.

Retired Coast Guard Adm. Thad Allen, the Obama administration's point man on the disaster, said the government gave the go-ahead after carefully reviewing the risks.

"What we didn't want to do is compound that problem by making an irreversible mistake," he said at the end of a 24-hour roller-coaster of hopes raised, hopes dashed and hopes raised again along the Gulf Coast.

The cap — a 75-ton metal stack of pipes and valves — was lowered onto the well on Monday in hopes of either bottling up the oil inside the well machinery, or capturing it and funneling it to the surface. But before BP could test the equipment, the government intervened because of second thoughts about whether the buildup of pressure from the gushing oil could rupture the walls of the well and make the leak worse.

"We sat long and hard about delaying the tests," Allen said. He said that the pause was necessary in the interest of the public, the environment and safety, and that officials were convinced the test could go forward.

A prelude to the test began with BP shutting off pipes that were funneling some of the oil to ships on the surface so the full force of the gusher went up into the cap. Then deep-sea robots began slowly closing, one at a time, three openings in the cap that let oil pass through. Ultimately, the flow of crude will be blocked entirely. All along, engineers will be watching pressure readings to learn whether the well is intact.

Allen said BP will monitor the results every six hours and end the test after 48 hours to evaluate the findings

BP has been directed to carry out "additional seismic testing and monitoring from ROVs (remotely operated vehicles) as well as acoustic and temperature monitoring throughout the duration of the well integrity test," the White House said in a statement. "The test will take up to 48 hours and will include periodic assessments in 6-hour increments."

Earlier, Doug Suttles, BP chief operating officer of exploration and production, told CNN that "there were a couple of other concerns around ways flow could escape and we needed to go examine those before we proceeded."

An unstable area around the wellbore could create bigger problems if the leak continued elsewhere in the well after the cap valves were shut, experts said.

"It's an incredibly big concern," said Don Van Nieuwenhuise, director of Professional Geoscience Programs at the University of Houston. "They need to get a scan of where things are, that way when they do pressure testing, they know to look out for ruptures or changes."

Suttles said the government wanted to verify that the casing, or the piping in the well, is intact and that the oil would stay contained if BP caps the well with its 75-ton metal stack.

'A good precaution' to waitWells said earlier Wednesday that it was the government's call late Tuesday to re-evaluate plans for testing the new cap. "It's a good precaution for us to take at this time," Wells added. "We need to understand exactly what's going on."

The cap is a stopgap measure until a relief well can be drilled to then plug the blownout well. The relief well's timeframe has always been hazy, with company and federal officials giving estimates ranging from the end of July to the middle of August before it can be completed.

The test is designed to tell if oil leaking to the surface is coming from a single leak or if more leaks are present elsewhere in the well.

If it's the latter case, the company would leave the valves open on the cap and try to collect the oil with up to four vessels floating on the surface above. Allen said a bigger siphoning operation should be in place by Monday to collect all or most of the oil if it is not contained by the cap.

The oil giant had been scheduled to start slowly shutting off valves Tuesday on the cap, aiming to stop the flow of oil for the first time in three months.

A series of methodical, preliminary steps were completed before progress stalled. Engineers spent hours on a seismic survey, creating a map of the rock under the sea floor to spot potential dangers, like gas pockets. The map also provides a baseline to compare with later surveys during and after the test to see if the pressure on the well is causing underground problems.

Allen late Tuesday met with the federal energy secretary and the head of the U.S. Geological Survey as well as BP officials and other scientists after the mapping was done.

"As a result of these discussions, we decided that the process may benefit from additional analysis," Allen said.

Marine food web alteredAs attempts to stop the leak continued, scientists reported early signs that the spill was altering the marine food web by killing or tainting some creatures and spurring the growth of others more suited to a fouled environment.

Near the spill site, researchers have documented a massive die-off of pyrosomes — cucumber-shaped, gelatinous organisms fed on by endangered sea turtles.

Along the coast, droplets of oil are being found inside the shells of young crabs that are a mainstay in the diet of fish, turtles and shorebirds.

And at the base of the food web, tiny organisms that consume oil and gas are proliferating.

If such impacts continue, the scientists warn of a grim reshuffling of sealife that could over time cascade through the ecosystem and imperil the region's multibillion-dollar fishing industry.
Along the Gulf Coast, where the spill has heavily damaged the region's vital tourism and fishing industries, people anxiously awaited the outcome of the painstakingly slow work.

"I don't know what's taking them so long. I just hope they take care of it," said Lanette Eder, a vacationing school nutritionist from Hoschton, Ga., who was walking on the white sand at Pensacola Beach, Fla.

The Blue Dolphin, left, and the HOS Centerline, the ships supplying the mud for the static kill operation on the Helix Q4000, are seen delivering mud through hoses at the site of the Deepwater Horizon Oil Spill in the Gulf of Mexico, off the coast of Louisiana, on Aug. 3, 2010. In the background is the Development Driller III, which is drilling the primary relief well.
(Gerald Herbert / AP)
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Eddie Forsythe and Don Rorabough dump a box of blue crabs onto a sorting table at B.K. Seafood in Yscloskey, La., on Aug. 3, 2010. The crabs were caught by fisherman Garet Mones. Commercial and recreational fishing has resumed, with some restrictions in areas that were closed by the Deepwater Horizon oil spill.
(Chuck Cook / AP)
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Sea turtle hatchlings that emerged from eggs gathered on the northern Gulf Coast of Florida are released at Playalinda Beach on the Canaveral National Seashore near Titusville, Fla., on Aug. 2, 2010. The sea turtles were born at a Kennedy Space Center incubation site, where thousands of eggs collected from Florida and Alabama beaches along the Gulf of Mexico have been sent.
(Craig Rubadoux / Florida Today via AP)
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A crab, covered with oil, walks along an oil absorbent boom near roso-cane reeds at the South Pass of the Mississippi River in Plaquemines Parish, Louisiana on Aug. 1, 2010. BP is testing the well to see if it can withstand a "static kill" which would close the well permanently.
(Pool / Reuters)
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A boat motors through a sunset oil sheen off East Grand Terre Island, where the Gulf of Mexico meets Barataria Bay on the La. coast, on the evening of July 31.
(Gerald Herbert / AP)
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Oil approaches a line of barges and boom positioned to protect East Grand Terre Island, partially seen at top right, on July 31.
(Gerald Herbert / AP)
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Oil from the Deepwater Horizon oil spill is seen near an unprotected island in the Gulf of Mexico near Timbalier Bay, off the coast of Louisiana on Wednesday, July 28.
(Gerald Herbert / AP)
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Greenpeace activists stand outside a BP gas station in London, England, on July 27 after they put up a fence to cut off access. Several dozen BP stations in London were temporarily shut down to protest the Gulf spill.
(Leon Neal / AFP - Getty Images)
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James Wilson sells T-shirts to those arriving in Grand Isle, La., for the music festival Island Aid 2010 on July 24.
(Dave Martin / AP)
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Activists covered in food coloring made to look like oil protest BP's Gulf oil spill in Mexico City on July 22. The sign at far left reads in Spanish "Petroleum kills animals."
(Alexandre Meneghini / AP)
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People in Lafayette, La., wear "Keep Drilling" tee shirts at the "Rally for Economic Survival" opposing the federal ban on deepwater drilling in the Gulf of Mexico on Wednesday, July 21. Supporters at the rally want President Obama to lift the moratorium immediately to protect Louisiana's jobs and economy.
(Ann Heisenfelt / EPA)
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A flock of white ibis lift off from marsh grass on Dry Bread Island in St. Bernard Parish, La., July 21. Crews found about 130 dead birds and 15 live birds affected by oil from the Deepwater Horizon oil spill on July 19 in the eastern part of the parish behind the Chandeleur Islands.
(Patrick Semansky / AP)
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Kenneth Feinberg, administrator of the BP Oil Spill Victim Compensation Fund testifies during a hearing before the House Judiciary Committee on July 21 in Washington, D.C. The hearing was to examine the claim process for victims of the Gulf Coast oil spill.
(Alex Wong / Getty Images)
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An American white pelican has its wings checked during a physical examination at Brookfield Zoo’s Animal Hospital by Michael Adkesson and Michael O’Neill on July 21. The bird, along with four other pelicans, was rescued from the Gulf Coast oil spill and will be placed on permanent exhibit at the zoo.
(Jim Schulz / Chicago Zoological Society via AP)
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Native people of the Gwich'in Nation form a human banner on the banks of the Porcupine River near Ft. Yukon, Alaska July 21, in regard to the BP oil spill with a message to protect the Arctic National Wildlife Refuge from oil development. The images include a Porcupine caribou antler and a threatened Yukon River Salmon.
(Camila Roy / Spectral Q via Reuters)
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Editor's note:
This image contains graphic content that some viewers may find disturbing.